When drilling a well, a borehole is typically drilled from the earth's surface to a selected depth and a string of casing is suspended and then cemented in place within the borehole. A drill bit is then passed through the initial cased borehole and is used to drill a smaller diameter borehole to an even greater depth. A smaller diameter casing is then suspended and cemented in place within the new borehole. This is repeated until a plurality of concentric casings are suspended and cemented within the well to a depth, which causes the well to extend through one or more hydrocarbon producing formations.
Rather than suspending a concentric casing from the bottom of the borehole to the surface, a liner is often suspended adjacent to the lower end of the previously suspended casing, or from a previously suspended and cemented liner, so as to extend the liner from the previously set casing or liner to the bottom of the new borehole. A liner is defined as casing that is not run to the surface. A liner hanger is used to suspend the liner within the lower end of the previously set casing or liner.
A running and setting tool disposed on the lower end of a work string may be releasably connected to the liner hanger, which is attached to the top of the liner. The work string lowers the liner hanger and liner into the open borehole until the liner hanger is adjacent the lower end of the previously set casing or liner, with the lower end of the liner typically slightly above the bottom of the open borehole. When the liner reaches the desired location relative to the bottom of the open borehole and the previously set casing or liner, a setting mechanism is conventionally actuated to move an anchoring element (e.g., slips) on the liner hanger from a compressed position to an expanded position and into engagement with the previously set casing or liner. Packer elements are also included in liner hanger systems to seal the annulus between the liner and the previously set casing. Such packer elements may be radially set by axial movement of the packer element relative to a conical wedge ring (or packer cone) on the liner hanger. An actuator on the liner hanger causes the packer element to move axially with respect to the conical wedge ring and thereby expand into sealing engagement with the casing surface to be sealed.
In conventional liner hanger systems, the packer is often located above the slips of the liner hanger. However, in such arrangements, the liner hanger body proximate the slips includes multiple grooves and slots that can weaken the mandrel and lead to lower burst and collapse ratings of the liner.